1. Field of the Invention
The present invention relates to an electrostatic actuator, a liquid discharge head, a liquid cartridge, an imaging apparatus, a micro pump, and an optical device.
2. Description of the Related Art
A liquid discharge head used in an inkjet recording apparatus such as a printer, a facsimile machine, a copying machine, or a plotter, includes nozzles that discharge liquid droplets, liquid chambers that are connected to the nozzle (also referred to as discharge chamber, pressure chamber, pressurized liquid chamber, or ink flow path, for example), and actuator elements that generate energy for pressurizing the ink contained within the liquid chambers. With the generated energy, the liquid discharge head applies pressure to recording liquid contained within the liquid chamber, and induces liquid droplets to be discharged from the nozzle.
The liquid discharge head may employ a piezoelectric actuator as an electromechanical transducer, a thermal actuator that utilizes film boiling as an electrothermal transducer, or an electrostatic actuator that utilizes electrostatic force between an oscillating plate and an electrode, for example. It is noted that a liquid discharge head that employs an electrostatic actuator is particularly preferred in consideration of its possibilities with respect to miniaturization, speed increase, high densification, and energy conservation. Accordingly, attempts are currently being made to further develop such a liquid discharge head.
It is noted that the characteristics of the liquid discharge head that uses the electrostatic actuator are greatly affected by the degree of dimensional accuracy (height consistency) in the gaps formed between an oscillating plate and an electrode layer. It is particularly noted that when large-scale variations occur in the characteristics of actuators of an inkjet head (liquid discharge head), printing accuracy and image quality reproducibility may be significantly degraded. Also, the gap dimension (height) is preferably arranged to be around 0.1-0.5 μm in order to enable voltage reduction. Accordingly, higher dimensional accuracy is demanded in the inkjet head (liquid discharge head).
Japanese Laid-Open Patent Publication No. 11-263012 discloses an inkjet head that is fabricated by bonding together a substrate (cavity plate) on which pressurized liquid chambers and an oscillating plate are formed and a substrate (glass plate) on which recessed portions corresponding to gaps (oscillating chambers) and segment electrodes are formed.
In such an inkjet head that is constructed by bonding two substrates to create gaps between the oscillating plate and the electrodes, relatively large-scale dimensional variations occur with respect to the height (length) of the gaps owing to dimensional variations that are created during various processing stages including recessed portion formation, electrode formation, and bonding, for example. As a result, it is difficult to obtain an actuator with high accuracy and high reliability in this example.
Japanese Laid-Open Patent Publication No. 2001-18383 discloses an inkjet head that is fabricated by forming on a first substrate individual electrodes and an oscillating plate arranged opposite the individual electrodes via gaps formed by sacrificial layer etching; forming grooves corresponding to pressure chambers on a second substrate; and bonding the second substrate to the first substrate to thereby reduce dimensional variations in the gap height.
It is noted that in an electrostatic actuator, a connection path for interconnecting gaps and introducing air therein is provided in order to reduce the difference between the pressure within the gap and the atmospheric pressure and improve actuator reliability.
For example, Japanese Laid-Open Patent Publication No. 11-263012 discloses depositing a hydrophobic film on the internal sides of the oscillating chambers (gaps) between the oscillating plate and the electrodes by interconnecting the oscillating chambers to a connection path that is connected to the exterior of the actuator, introducing gas for forming the hydrophobic film into the oscillating chambers via the connection path, and sealing the connection path with a sealing member thereafter.
In this case, to efficiently introduce the gas for fabricating the hydrophobic film within the oscillating chambers, the cross-sectional area of the connection path is preferably arranged to be large. In this regard, for example, Japanese Laid-Open Patent Publication No. 2003-72070 discloses digging into an electrode substrate having recessed portions and electrodes formed thereon to increase the cross-sectional area of the connection path.
It is noted that Japanese Laid-Open Patent Publication No. 2001-18383 discloses use of a sacrificial layer etching process to fabricate an oscillating plate, gaps, and electrodes on one substrate, a sacrificial layer etch hole has to be sealed after the sacrificial layer etching process. For example, Japanese Laid-Open Patent Publication No. 2001-18383 discloses sealing such a hole with an insulating film made of silica dioxide. However, a CVD process, which is performed under a vacuum environment, is generally used to deposit silica dioxide, and in this case, the pressure within the gap becomes lower than the atmospheric pressure after the sacrificial etch hole is hermetically sealed. As a result, the oscillating plate may be recessed toward the electrode side. Thus, the gap has to be exposed to the atmosphere afterwards so that the deformation of the oscillating plate may be corrected. Also, as is described above, a connection path has to be provided in order to introduce gas for fabricating a hydrophobic film inside the gap.
In the case of connecting the gap to the exterior via the connection path for exposing the gap to the atmosphere or introducing material gas of the hydrophobic film, a hole connecting the connection path to the atmosphere has to be sealed with a sealing agent after the atmosphere exposure or gas introduction in order to prevent moisture or dust particles from entering the gap.
However, in the case of sealing the atmosphere connecting hole with a sealing agent, the sealing agent may penetrate into the gap via the connection path due to the capillary effect since the connection path connecting the atmosphere connecting hole to the gap is very fine. When the sealing agent penetrates into the gap as is described, normal operations may be hampered.